Electrically insulating joints for high-pressure pipelines

ABSTRACT

An electrically insulating joint between two electrically conducting pipe which in use are at different electrical potentials, wherein the pipes are clamped to opposite ends of an insulating spacer sleeve with metal collars interposed between the ends of the sleeve and the pipes, and at least the one of the collars which is anodic with respect to the other being formed of a metal such as titanium which forms a protective insulating skin under electrolytic action and thereby reduces the rate of galvanic corrosion.

Elite States Ptent avidson et al.

1451 Dec. 12,1972

1541 ELECTRICALLY INSULATING JOINTS 3,133,873 5/1964 Miller et al...204/196 FOR HIGH-PRESSURE PIPELINES FOREIGN PATENTS OR APPLICATIONS[72] Inventors: David Fulton Davidson, I-Iale Barns; l 1 0 0 7 4/ 969 GtB w 285/53 rea n in ggg g fi Irvmg Sale both of 567,159 1/1945 GreatBritain ..2s5/52 [73] Assignee: Associated Electrical Industries PrimaryExaminer-Thomas F. Callaghan Limited, London, England AttorneyLarson,Taylor & l-Iinds [22] Filed: Feb. 20, 1970 [57] ABSTRACT [21] Appl 13143An electrically insulating joint between two electrically conductingpipe which in use are at different 52 US. Cl ..2ss/53, 285/55 electricalPotentials, wherein the P p are clamped to 51] 1m. (:1. ..F16l 19/02,F161 58/00 Opposite ends of an insulating spacer sleeve with metal 5Field of Search "285/53, 52, 50 48, 47, 54 collars interposed betweenthe ends of the sleeve and 285/55. 204/196 290 the pipes, and at leastthe one of the collars which is anodic with respect to the other beingformed of a [56] References Cited metal such as titanium which forms aprotective insulating skin under electrolytic action and thereby UNITEDSTATES PATENTS reduces the rate of galvanic corrosion.

3,081,252 3/1963 Preiser et al ..204/290 X 7 Claims, 1 Drawing Figurelff/fl/f-JI 3 6' 34/572 1 1 1x /1 1,, W F AWW/ o A L Y/ m 9VELECTRICALLY INSULATING JOINTS FOR HIGH- PRESSURE PIPELINES Thisinvention relates to electrically insulating joints for high-pressurepipelines.

It is known for the windings of an electrical machine, for example thefield windings on the rotor of a turbogenerator, to be directly cooledby circulating a cooling liquid through the windings, which are in theform of electrically conducting pipes. It may be necessary to connecttogether two such pipes which in operation of the machine are atdifferent electrical potentials, for example to connecta cooling liquidmanifold which is at earth potential to the turns of the winding whichare at different potentials, and for this purpose it is necessary forthe joint between the two pipes to be electrically insulating. Inaddition, when the joint is in a moving part of the machine it isnecessary for it to be able to withstand the pressures developed in thecooling liquid by centrifugal force, which may be very high, as well asany mechanical vibration present. The joint must also be able towithstand the temperatures at which the machine operates.

One such electrically insulating joint is described in British Pat.Specification No'. 1,150,047, and comprises a substantially rigid,electrically insulating, pressure resistant spacer sleeve interposedbetween end portions of increased external diameter of the two pipes,and a clamping sleeve electrically insulated from at least one of saidpipes and having at one end a portion of reduced internal diameter andat the other end a clamping nut, by means of which clamping sleeve thesaid end portions are pressed in liquid-tight manner against the endfaces of the spacer sleeve. Sealing rings may be provided in recessesbetween the end portions and the spacer sleeves.

If the conductive pipes are at a different electrical potential, as maybe the case in operation of the machine, the conductivity of the coolingliquid may be such that electrolytic action will take place in thecooling liquid between the two conducting pipes. Although demineralizedwater may be used as cooling liquid, since this has a low electricalconductivity, there may still be a small leakage current between thepipes, and this may eventually cause galvanic corrosion at that pipewhich is anodic with respect to the other. This corrosion may eventuallylead to failure of one of the liquid-tight seals.

One object of the present invention is to provide protection againstsuch corrosion.

According to the invention, an electrically insulating joint between twoelectrically conducting pipes for conducting a liquid at high pressurewhich in use are at different electrical potentials, comprises a rigid,pressure-resistant and electrically insulating spacer sleeve the endfaces of which are respectively in liquid-tight relationship with a pairof metal collars which in turn are respectively in liquid-tightrelationship with the end of the two pipes, at least the one of saidcollars which is anodic with respect to the other in use of thearrangement being in contact with the liquid and being of a metal whichforms under electrolytic action a protective skin which is highlyresistant to the flow of electric current, thereby reducing the rate ofgalvanic corroson.

Said metal is preferably titanium, although other suitable metals areTantalum, Niobium, Zirconium, Vanadium, l-lafnium. It will be understoodthat the term metal includes alloys of titanium with any of thesealternative metals or alloys of any of these metals containing otherelements to improve specific properties such as mechanical strength.

The pipes may be formed with end portions of enlarged external diameterand be surrounded by a clamping sleeve electrically insulated from atleast one of the two pipes, the clamping sleeve having at one end aportion of reduced internal diameter and at the other end a clamping nutarranged to urge the two enlarged end portions of the pipes inwardstowards the spacer sleeve.

In such an arrangement the said collars may be of greater externaldiameter than the pipes and be attached to the respective pipes, forexample by welding or brazing, to form the said enlarged end portions,the collars being pressed in a liquid-tight manner against therespective end faces of the spacer sleeve by the clamping sleeve.

Alternatively the collars may be separate from the pipes and interposedbetween the ends of the spacer sleeve and the respective ends of thepipes, the clamping sleeve pressing the pipes against the collars andthe collars against the spacer sleeve ina liquid-tight manner. Thisalternative arrangement has the advantage that. the collars may bereplaced if necessary without disturbing the pipework. In thealternative arrangement, theenlarged ends of the pipes may be formed byferrules secured to the pipes and of the same material as the collars.

One electrically insulating joint in accordance with the invention willnow be described, by way of example, with reference to the accompanyingdrawing, which is a diagrammatic cross-sectional view of the joint.

Referring to the figure, two pipes, l and 2, forming hydraulicconnections to part of the field windings on the liquid-cooled rotor ofa turbo-generator, have end portions 3, 4 of enlarged external diameterformed by titanium ferrules brazed on to the ends of the respectivepipes. Between the two end portions 3 and 4 are held, in order, atitanium collar 5, a ceramic spacer sleeve 6, and another titaniumcollar 7, each being of the same cross-section as the end portions 3, 4.Each end face of each of the collars 5, 7 has an annular groove in whicha sealing ring 8 is located. The ceramic sleeve 6 is conveniently asintered oxide material, and the sealing rings 8 are conveniently 0rings of an ageing-resistant plastics material.

The end portions 3, 4 the collars 5, 7 and the sleeve 6 are surroundedby and clamped together by a clamping sleeve 9 which has at one end aportion 10 of reduced internal diameter which bears via a ceramic bush11 upon the portion 3; of enlarged external diameter of the first pipe1, and at the other end a clamping nut 12 engaging with a threadedportion 13 of the sleeve 9 and bearing upon the portion 4. The sleeve 9is lined over its length between the portion 10 and the nut 12 with theinsulating layer 14 of heat-stabilized polyester film, and the firstpipe 1 is covered with a layer of insulating material 15, shrunk on tothe pipe.

The first pipe 1 is connected'hydraulically and electrically to one ofthe turns of the field windings, and the second pipe 2 is part of acooling liquid manifold supplying demineralized water to the fieldwindings via the first pipe 1, and is at earth potential. Thus inoperation of the turbo-generator the first pipe 1 is at a higher voltagethan the second pipe 2 and the nut 12 and the sleeve 9 will be at thesame voltage as the second pipe 2, being insulated from the first pipe 1by means of the layers 14, 1S and the bush 11. The layers 14, 15 arelong enough to prevent creepage current over their surfaces.

Thus the pipes 1, 2 are connected by an electrically insulating joint,and the surfaces which are most liable to electrolytic action are oftitanium and are thereby protected by the insulating film which forms onthe titanium. It will be understood that the leakage current variesapproximately inversely with the distance between the pipes. Therefore,after the protective film has formed the resistance of the leakage pathin the liquid is increased which reduces this current to a value whichdoes not cause appreciable damage. The lifetime of the joints is thusincreased considerably, but if necessary, the collars 5, 7 may readilybe replaced without disturbing the pipes l, 2. It will be appreciatedthat there the voltage is only applied in one direction, as in thearrangement described, only the anodic side need be protected in thisway, although it may be more convenient to manufacture both sides in thesame way.

Moreover if it is considered advisable additional protection can beobtained by making the pipes l and 2 entirely of titanium or making atleast several inches of the pipe which is anodic of titanium.

We Claim:

1. An electrically insulating joint comprising two electricallyconducting pipes for conveying a liquid at high pressure and which inuse are at different electrical potentials, said pipes having endportions of enlarged external diameter, a rigid pressure-resistant andelectrically-insulating spacer sleeve between the enlarged ends of thepipes, a pair of collars separate from the pipes each interposed betweenthe end of a respective pipe and the adjacent end of the spacer sleeve,and a clamping sleeve surrounding the enlarged ends of the two pipes andelectrically insulated from at least one of the pipes, said clampingsleeve including at one end a portion of reduced internal diameter, saidjoint further comprising a clamping nut at the other end of saidclamping sleeve for urging the two enlarged end portions inwards topress the pipes against the collars and the collars against the spacersleeve in a liquid-tight manner to form the joint, at least the one ofsaid collars which is anodic with respect to the other in use of thearrangement being in contact with the liquid and being of a metal whichforms under electrolytic action a protective skin which is highlyresistant to the flow of electric current, thereby reducing the rate ofgalvanic corrosion.

2. An electrically insulating joint according to claim 1, wherein theenlarged ends of the pipes are formed by ferrules secured to the pipes.

3. An electrically insulating joint according to claim 2, wherein theferrules are of the same material as the collars.

4. An electrically insulating joint according to claim 3, wherein bothcollars and both ferrules are of titani- 5. An electrically insulatingjoint according to claim 1, wherein each end surface of each of thecollars is formed with an annular groove containing a sealing ring whichis clamped against the adjacent end surface of the spacer sleeve or endof a pipe as the case may be.

6. An electrically insulating joint according to claim 5, wherein thesealing rings are of plastics material.

7. An electrically insulating joint according to claim 1 for conveyinghigh pressure liquid coolant between a manifold and a fieldwinding of aturbo generator.

1. An electrically insulating joint comprising two electricallyconducting pipes for conveying a liquid at high pressure and which inuse are at different electrical potentials, said pipes having endportions of enlarged external diameter, a rigid pressure-resistant andelectrically-insulating spacer sleeve between the enlarged ends of thepipes, a pair of collars separate from the pipes each interposed betweenthe end of a respective pipe and the adjacent end of the spacer sleeve,and a clamping sleeve surrounding the enlarged ends of the two pipes andelectrically insulated from at least one of the pipes, said clampingsleeve including at one end a portion of reduced internal diameter, saidjoint further comprising a clamping nut at the other end of saidclamping sleeve for urging the two enlarged end portions inwards topress the pipes against the collars and the collars against the spacersleeve in a liquidtight manner to form the joint, at least the one ofsaid collars which is anodic with respect to the other in use of thearrangement being in contact with the liquid and being of a metal whichforms under electrolytic action a protective skin which is highlyresistant to the flow of electric current, thereby reducing the rate ofgalvanic corrosion.
 2. An electrically insulating joint according toclaim 1, wherein the enlarged ends of the pipes are formed by ferrulessecured to the pipes.
 3. An electrically insulating joint according toclaim 2, wherein the ferrules are of the same material as the collars.4. An electrically insulating joint according to claim 3, wherein bothcollars and both ferrules are of titanium.
 5. An electrically insulatingjoint according to claim 1, wherein each end surface of each of thecollars is formed with an annular groove containing a sealing ring whichis clamped against the adjacent end surface of the spacer sleeve or endof a pipe as the case may be.
 6. An electrically insulating jointaccording to claim 5, wherein the sealing rings are of plasticsmaterial.
 7. An electrically insulating joint according to claim 1 forconveying high pressure liquid coolant between a manifold and a fieldwinding of a turbo generator.